This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-160879, filed Jun. 8, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a liquid crystal lens device, which can change its focus position by varying the electric field strength.
A liquid crystal lens device of this type is described, for example, in U.S. Pat. No. 4,190,330 entitled xe2x80x9cVariable Focus Liquid Crystal Lens System.xe2x80x9d
This liquid crystal lens device comprises a first body including a birefringent nematic liquid crystal material oriented in a first direction, a second body including a birefringent nematic liquid crystal material oriented in a second direction perpendicular to the first direction, a pair of electrodes for applying electric fields with components perpendicular to the first and second directions to the first and second bodies, and means for varying the electric field strength.
When no electric fields are applied to the first and second bodies, with respect to components of light polarized perpendicular to the first direction of the incident end of the first body, included in incident light, the first body serves as a medium having an ordinary index of the liquid crystal material, and the second body as a medium having an extraordinary index of the liquid crystal material. With respect to components of light polarized parallel to the first direction of the incident end of the first body, in contrast with this, the first body serves as a medium having an extraordinary index of the liquid crystal material, and the second body as a medium having an ordinary index of the liquid crystal material.
When the electric fields are applied to the first and second bodies with use of the means for varying the electric field strength, either of the first and second bodies serves as a medium having an ordinary index of the liquid crystal material.
Thus, in the liquid crystal lens device, the index can be changed by varying the electric field strength, so that the focus position can be changed without mechanically moving any parts of the device.
Endoscopes require use of a variable focus system, which ensures continual production of clear images such that the affected part can be diagnosed more accurately.
A modern endoscope reduced much in diameter has so narrow a space that it is hard for an imaging optical system holding member in the distal end portion of the endoscope to contain a variable focus system based on mechanical means. Preferably, therefore, the variable focus system should comprise electrical means including no mechanically-operated parts. The aforementioned liquid crystal lens device can be an example of potent electrical means.
The wall thickness of the imaging optical system holding member is made as thin as possible to reconcile the reduced diameter and the maximum volume of emission. In order to secure the necessary minimum stiffness of the optical system holding member, therefore, it is advisable to minimize the size of notches in the holding member for mounting a liquid crystal lens. Thus, it is to be desired that the liquid crystal lens device, which is intended to be built in an endoscope, should have a compact external shape involving fewer projections.
For example, the small-diameter endoscope has an outside diameter of about 13 mm, and the imaging optical system holding member to be incorporated therein has an outside diameter of about 4.5 mm and an overall length of about 10 mm. Thus, the liquid crystal lens itself is expected to have a diameter of about 2 mm and a thickness of about 0.5 mm.
The present invention has been contrived in consideration of these circumstances, and its object is to provide a liquid crystal lens device adapted to be incorporated in a narrow cylindrical member.
The liquid crystal lens device described herein is supposed to include a simple liquid crystal lens, a liquid crystal lens unit comprising the liquid crystal lens and a wiring board attached thereto, and a liquid crystal lens assembly comprising the liquid crystal lens unit and a lens frame supporting the same.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.